Examples borrowed from this GraphViz Pocket Reference and its underlying Git repository.

Example 1: Simple Graph

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/e4a72d37c637c75e9afb795fbcc10ba4.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 graph {
    3     rankdir = LR;
    4 
    5     a -- b;
    6     b -- c;
    7     a -- c;
    8     d -- c;
    9     e -- c;
   10     e -- a;
   11 }
   12 

---

Example 2: K6

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/9a84152a35d27f27e7149e923f9866ac.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 graph {
    3     a -- b;
    4     b -- c;
    5     c -- d;
    6     d -- e;
    7     e -- f;
    8     a -- f;
    9     a -- c;
   10     a -- d;
   11     a -- e;
   12     b -- d;
   13     b -- e;
   14     b -- f;
   15     c -- e;
   16     c -- f;
   17     d -- f;
   18 }
   19 

---

Example 3: Simple Digraph

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/001ea88d2251d89b985c4223fb1cbe3c.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 digraph {
    3     a -> b;
    4     b -> c;
    5     c -> d;
    6     d -> a;
    7 }
    8 

---

Example 4: Full Digraph

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/2cd7b0fa6060296368c696dd93890d04.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 digraph {
    3     a -> b[label="0.2",weight="0.2"];
    4     a -> c[label="0.4",weight="0.4"];
    5     c -> b[label="0.6",weight="0.6"];
    6     c -> e[label="0.6",weight="0.6"];
    7     e -> e[label="0.1",weight="0.1"];
    8     e -> b[label="0.7",weight="0.7"];
    9 }
   10 

---

Example 5: Showing A Path

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/dbebe10e6bc6fe4eb6d5895923ed8b4e.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 graph {
    3     a -- b[color=red,penwidth=3.0];
    4     b -- c;
    5     c -- d[color=red,penwidth=3.0];
    6     d -- e;
    7     e -- f;
    8     a -- d;
    9     b -- d[color=red,penwidth=3.0];
   10     c -- f[color=red,penwidth=3.0];
   11 }
   12 

---

Example 6: Subgraphs

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/86ed055985d9435b90b7855d367714d0.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 digraph {
    3     subgraph cluster_0 {
    4         label="Subgraph A";
    5         a -> b;
    6         b -> c;
    7         c -> d;
    8     }
    9 
   10     subgraph cluster_1 {
   11         label="Subgraph B";
   12         a -> f;
   13         f -> c;
   14     }
   15 }
   16 

---

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kcirco' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/f53d6274166be3fe1ddf26eda4f6862c.svg'
Output: 
There is no layout engine support for "circo"
Use one of:

Original DOT:
    1 
    2 graph {
    3     splines=line;
    4     subgraph cluster_0 {
    5         label="Subgraph A";
    6         a; b; c
    7     }
    8 
    9     subgraph cluster_1 {
   10         label="Subgraph B";
   11         d; e;
   12     }
   13 
   14     a -- e;
   15     a -- d;
   16     b -- d;
   17     b -- e;
   18     c -- d;
   19     c -- e;
   20 }
   21 

---

Example 7: Large Graphs

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kdot' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/1ba6010a9b3644181182f4115f7d0199.svg'
Output: 
There is no layout engine support for "dot"
Perhaps "dot -c" needs to be run (with installer's privileges) to register the plugins?

Original DOT:
    1 
    2 graph {
    3     rankdir=LR; // Left to Right, instead of Top to Bottom
    4     a -- { b c d };
    5     b -- { c e };
    6     c -- { e f };
    7     d -- { f g };
    8     e -- h;
    9     f -- { h i j g };
   10     g -- k;
   11     h -- { o l };
   12     i -- { l m j };
   13     j -- { m n k };
   14     k -- { n r };
   15     l -- { o m };
   16     m -- { o p n };
   17     n -- { q r };
   18     o -- { s p };
   19     p -- { s t q };
   20     q -- { t r };
   21     r -- t;
   22     s -- z;
   23     t -- z;
   24 }
   25 

---

Error generating Graphviz image:

Graphviz cannot generate graph
Command: /usr/bin/dot '-Kdot' '-Tsvg' '-o/data/blog.flirble.org/wp-content/tfo-graphviz/fdb2460d44d05fd67dc0127525910f62.svg'
Output: 
There is no layout engine support for "dot"
Perhaps "dot -c" needs to be run (with installer's privileges) to register the plugins?

Original DOT:
    1 
    2 graph {
    3     rankdir=LR;
    4     a -- { b c d }; b -- { c e }; c -- { e f }; d -- { f g }; e -- h;
    5     f -- { h i j g }; g -- k; h -- { o l }; i -- { l m j }; j -- { m n k };
    6     k -- { n r }; l -- { o m }; m -- { o p n }; n -- { q r };
    7     o -- { s p }; p -- { s t q }; q -- { t r }; r -- t; s -- z; t -- z;
    8     { rank=same; b, c, d }
    9     { rank=same; e, f, g }
   10     { rank=same; h, i, j, k }
   11     { rank=same; l, m, n }
   12     { rank=same; o, p, q, r }
   13     { rank=same; s, t }
   14 }
   15 

---